Plastic article or earthenware shaping or treating: apparatus – Product or preform repair or restoring means – Tire recapping – rebeading or sidewall replacing means
Patent
1997-02-13
1998-06-16
Mackey, James P.
Plastic article or earthenware shaping or treating: apparatus
Product or preform repair or restoring means
Tire recapping, rebeading or sidewall replacing means
425 22, 425 24, 425 25, 425 39, B29D 3006
Patent
active
057666440
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to an arrangement in the production of air-filled tires.
More specifically the present invention has to do with a pressure-compression mould, that is to say a vulcanisation mould, for the vulcanisation of tires.
The present invention has especially to do with the last step, that is to say the vulcanisation step, during the production of tires, and relates particularly to the reuse of old worn down tires during the utilisation of a recapping or tread application process.
When the wearing surface of a tire is worn down, for example down towards the pattern depth which the authorities accept, the tire can be used again on recapping or applying a tread.
On recapping, the tread is completely ground away. That is to say that all the old design is completely removed down to fresh rubber and without damaging the cord in the casing. A portion of the old rubber on the sides of the tire can also be removed. By dissimilar techniques, a new unvulcanised tread can be applied. On the sidewalls there can also be deposited a thin layer of unvulcanised rubber. After the tread is applied, a flexible tube can be placed inside the tire, if desired the vulcanisation mould comprising a bellows or being tubeless. The mould is heated in advance to about ca. 150.degree.-170.degree. C. by conducting heated steam through ducts in the mould, if desired the mould being heated by electrical resistance heating. When the raw tire is heated and is pressed out at the same time against the walls of the mould by supplying an internal pressure, the newly applied rubber material in the tire is moulded and vulcanised, the rubber mixture being converted from a mouldable plastic material to a solid elastic material.
Vulcanising is the description of the chemical reaction which occurs between the rubber material and sulphur under the influence of high temperature and pressure. The time which is needed to complete the vulcanisation process is dependent on both the pressure, temperature and the thickness of the rubber during vulcanisation. During the day's automobile tire production, zinc oxide, stearic acid and other compounds which accelerate the vulcanisation are also added to the rubber mixture, besides sulphur.
Based on the above, there can also be used, for recapping automobile tires, factory-ready treads which are adapted for the different tire dimensions and breadths and which have a finished design and are ready vulcanised. On the finished worn down tire casing, a thin layer of unvulcanised bonding rubber is first placed, and on the outside there is drawn a sleeve (envelope). The vulcanisation itself takes place by putting the entire tire in an autoclave where it is supplied with pressure and it is heated to a temperature of ca. 98.degree. C. Since the tread is vulcanised in advance it is only the bonding rubber which is to be vulcanised. This method is mentioned in U.S. Pat. No. 3,839,123.
When a tire is recapped thus by a heat vulcanisation as is indicated above, it is really the last step of the new tire manufacture which is repeated whereby the tread is renewed.
Even if the dimension designations and the diameters on the reconstructed tires are correct relative to the metal mould which the tires are to be vulcanised in, the volumes of the tires can be dissimilar as a consequence of variations in the length and shape of the sidewalls of the tires.
Thus, if the sidewalls of the vulcanisation mould do not agree with the sidewalls of the tire or the tire volume in this side portion, an undesirable deformation of the tire will arise during the vulcanisation. If the mould for example is dimensioned for a greater tire volume than the tire which is to be recapped, significant tensile forces will arise in the cord casing beyond those designed to be withstood. The danger is thereby great for permanent deformation of the tire to occur. This disagreement in volume between the side surface portions of the tire and the manufacturing mould leads to unfortunate deforming flows of the rubber material during the pressing.
Thi
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